In a process of preparing a hot beverage, a temperature of the extracting fluid is an important factor. This is particularly true in the case of a process of preparing coffee on the basis of a quantity of ground coffee beans as the quantity of the beverage extract and water as the extracting fluid. In such a case, in order to have a good extraction of the ground coffee beans, the water that is used in the coffee making process is heated, wherein the temperature of the water is increased such as to be in a predetermined range, for example, a range from 90° C. to 96° C.
Usually, coffee is prepared by using a coffee maker. A specific type of coffee maker is a coffee maker which is suitable for preparing quantities of coffee on the basis of coffee pads, i.e. envelopes filled with a quantity of ground coffee beans, wherein the envelopes are permeable to liquid. In general, such a coffee maker comprises a sealable brew chamber which is adapted to receive one or more coffee pads. During operation of the coffee maker, a quantity of hot water is forced to flow through the at least one coffee pad. In the process, the envelope of the coffee pad acts as a filter. In this way, on the basis of the interaction between the hot water and the coffee pad inside the brew chamber, a desired quantity of coffee is obtained.
A coffee maker as mentioned in the preceding paragraph is known from EP 0 771 542. For the purpose of heating water to a predetermined temperature, the known coffee maker comprises a heat exchanger having an electric resistor. During operation, water is instantly heated to the predetermined temperature while flowing through this heat exchanger. An electric pump is provided for realizing flows of water through the coffee maker, which are necessary in a process of making coffee. In order to accurately control the operation of the electric resistor of the heat exchanger and the operation of the pump, such that a predetermined temperature of water is obtained, the coffee maker comprises a temperature sensor for detecting the temperature reached by the water after having been heated by the heat exchanger and a control device which processes the signals received from the temperature sensor. Furthermore, a water delivery counter means is provided for measuring a quantity of water transferred to the brew chamber, and the control device is adapted to process simultaneously signals received from the temperature sensor and from the water delivery counter means. The signal received from the water delivery counter means is also suitable to be used for the purpose of controlling the quantity of coffee to be made. In the coffee maker known from EP 0 771 542, when it appears that water exiting the heat exchanger is at a temperature lower than the predetermined temperature, the pump delivery is reduced or interrupted until the water exiting the heat exchanger has recovered the predetermined temperature.